1. Technical Field
The invention relates generally to phase change memory, and more particularly, to an electrode and method for a phase change material of a phase change memory device.
2. Background Art
Phase change memory (PCM) is a type of non-volatile computer memory using a phase change material capable of resistance changes depending on the mechanical phase of the material. PCM may also be known as ovonic unified memory (OUM), chalcogenide random access memory (CRAM) or phase-change random access memory (PRAM). Almost all PCMs are built using a chalcogenide alloy, typically a mixture of germanium (Ge), antimony (Sb) and tellurium (Te), which is referred to as GST. One GST alloy has the formula: Ge2Sb2Te5. Under high temperature (over 600° C.), a chalcogenide becomes liquid and by subsequent rapid cooling it is frozen into an amorphous glass-like state and its electrical resistance is high. By heating the chalcogenide to a temperature above its crystallization point, but below the melting point, it will transform into a crystalline state with a much lower resistance. In addition, when the material is set to a particular state representing a resistance value, the value is retained until reset by another phase change of the material. The phase switching can be completed very quickly, e.g., under 10 ns. During use as a PCM, the phase of the phase change material is typically changed by heat created by a small pulse of electrical power.
As a result of the above properties, chalcogenide materials provide a promising mechanism for memories in next generation technology. In particular, the phase change materials can be easily integrated into conventional complementary metal-oxide semiconductor (CMOS) processing. PCMs also provide a number of advantages compared to conventional memories. For example, PCMs provide a significant space advantage over conventional static random access memory (SRAM) cell designs, do not need periodic refresh to retain information as with conventional dynamic random access memory (DRAM), and are more scalable than magnetic random access memory (MRAM).
A typical PCM cell includes a layer of chalcogenide material positioned between two electrically conducting electrodes. One challenge relative to PCMs, however, is providing adequate adhesion between the electrode material and the chalcogenide material. In many instances, the electrode material may include titanium nitride (TiN), which has a very poor adhesion to GST, resulting in delamination. Adhesion layers have also been employed such as disclosed in U.S. Pat. No. 6,744,088, which is hereby incorporated herein by reference.
There is a need in the art for a solution not available in the related art.